Panoramic Radiography Flashcards
what is tomography
technique allowing slices of the subject to be viewed separately
what are the two types of tomgraphy
conventional = one slice
computed = multiple slices
how is tomography produced
using different phenomena - x-rays/radio waves etc.,
what kind of tomography does panoramic radiographs use
linear tomography
what is linear tomography
the way of capturing a single, flat slice by moving the x-ray source and receptor past the area of interest during the exposure
what is the focal trough
thin band where images appear adequately sharp
where is the focal trough thinner
incisor region
why is the incisor region thinner in the focal trough
it is related to the speed of rotation at this point
what does orthogonal view mean
x-ray beam is more 90 degrees to the teeth
what are the advantages of an orthogonal view
reduces overlap of teeth to aid approximal caries assessment
improves angulation to more accurately represent interdental periodontal bone levels
what are the disadvantages of an orthogonal view
distorts rest of skeleton to varying degrees
narrower field of view so miss condyles
when is an orthogonal view appropriate
for cases requiring only caries or periodontal bone loss
in what direction relative to the focal trough do structures appear magnified
lingual to the focal trough
in what direction relative to the focal trough do structures appear smaller
buccal to the focal trough
if a subject is within the focal trough how much is it magnified by
about 25%
why are structures within the focal trough not distorted
the degree of horizontal magnification matches that vertically
how does distortion affect subjects buccal to the focal trough
appear narrower
how does distortion affect subjects lingual to the focal trough
appear broader
why do teeth get distorted if lingual or buccal to the trough
the beam sweeps from one side of the jaws to the other but x-ray source is always lingual to the focal trough
why are structures positioned further away from the receptor projected further up on the image
due to the angulation of the beam
what are the advantages of panoramic radiographs
can capture entire dentition in one image
able to image non-dental areas
lack of intra-oral holders benefits some patients
what are the disadvantages of panoramic radiographs
worse clarity
longer exposure time
higher radiation dose per image
what are the main components of the OPT machine
x-ray tubehead, receptor, control panel, patient positioning
how do you prepare the patient for an OPT
remove metal foreign bodies, position patient in machine, advise patient of tongue to roof of mouth, stand still, no swallowing
what apparatus helps to position the patient
bite peg, light beam markers, head grabber, chin rest
what is the correct positioning of the frankfurt plane and mid-sagittal plane
frankfurt - horizontal
mid-sagittal - centred in midline
what happens if the patient is too far forward in the machine
incisors are buccal to focal trough and appear narrower
what happens if the patient is too far backward in the machine
incisors now lingual to focal trough and appear wider
what are the instructions to the patient during the scan
stay still, press tongue up against palate, not talk or swallow
what are the appearance of movement artefacts affected by
direction of movement, duration of movement, speed of movement, timing of movement, structures moving
why is no lead apron used for dental radiography
it is not justified as the beam is not directed at the abdomen
what is on the quality standards checklist
patient preparation/instruction adequate
no patient positioning errors
correct anatomical coverage
good density and contrast
